1. Field of the Invention
The present invention relates to photolithographic equipment and to a method of exposing a substrate performed by such equipment in the manufacturing of semiconductor devices and the like. More particularly, the present invention relates to a device capable of discerning whether the correct reticle is transferred to an exposure apparatus of photolithographic equipment, to exposure equipment having such a device and to a method of exposing a substrate using an exposure apparatus of photolithographic equipment.
2. Description of the Related Art
Today's highly integrated semiconductor devices have multi-layered structures of thin films, which form circuit patterns of the devices, and insulating layers alternately disposed one atop the other. Such devices are formed by repeatedly processing and polishing a silicon wafer. The various processes that are performed on the wafer include photolithography, etching process, thin film deposition, and diffusion processes. Among these processes, photolithography is used to form a pre-designed circuit pattern on the silicon wafer. In general, photolithography entails coating the wafer with a layer of photoresist, exposing the photoresist, and developing the exposed photoresist.
In the exposure process, light, such as UV light, emitted from a light source is directed onto the wafer, on which the photoresist layer has been formed, via a photomask or a reticle (each of which will be referred to hereinafter generically as a “reticle”). The reticle bears a pattern corresponding to the circuit pattern to be formed on the wafer. The reticle is illuminated by the light. Thus, an image of the pattern of the reticle is picked up and transferred to the layer of photoresist. The exposure process is performed by an exposure apparatus such as a scanner or a stepper.
The multi-layered structure of a typical semiconductor device currently in the market may have tens of layers of circuit patterns. Therefore, tens of reticles may be used to manufacture a single semiconductor device. Therefore, one of the most important operations in performing a state-of-the-art exposure process is to check whether the reticles are being used in the correct sequence, i.e., whether the correct reticle is loaded in the exposure apparatus for each individual exposure process. However, it is very difficult to visually discriminate the reticles based on their patterns alone because the reticles often have the same size and similar patterns.
Accordingly, each conventional reticle has a barcode, and the exposure apparatus includes a barcode reader for discerning the barcodes. The barcode reader recognizes the barcode of each reticle to be loaded into the exposure apparatus to discern whether the reticle is appropriate for the exposure process that is about to be performed. Regardless, an exposure of a photoresist layer using the incorrect reticle may still occur in the conventional exposure equipment having a barcode reader.
First, the barcode itself may have a defect of a type that causes the reticle to be misidentified. As a result, the exposure process may be delayed or incorrectly performed due to barcode recognition errors.
Secondly, the barcode of a conventional reticle is located in a region surrounding the pattern of the reticle, i.e., in a peripheral region of the reticle. In this case, the barcode may be partially erased or contaminated. Thus, the barcode reader may incorrectly recognize the barcode or recognize nothing at all, thereby causing a delay or error in the exposure process.